Dual Daggers (PRC) PEACH.

[Kingreaper]

First thing to say: I like this idea, but what if there're more than two people in a party wanting the class?

Obviously, even two people requires enough people or the right kind of campaign. Makes an excellent NPC class too

Partners: If a Dual Dagger get’s separated from his partner, or if the partner dies and cannot be resurrected, they may train with a new partner who has at least one level in Dual Dagger. However, if the partners are of different Dual Dagger levels, they only get the class features available to the one with fewer Dual Dagger levels. This does not apply to their Sneak Attack class feature.

I don't like this as much, I feel the one with the more class levels should still be able to grant the bonuses to their partner, but not get them from the partner. (Or get them, but not grant them, dpending on your preference)

But I don't think it'd come up often so *meh*
Two-on-one: Like it.
Thieves’ Cant: Could the DC be partly based on bluff ranks (maybe 10+bluff-mod+class lvl) because as is, it's possible that just using bluff could work better than using the class ability.

Expert Cooperation: Makes sense to me.
Lingering Attack: Oooh, if they can get off one sneak attack they can both sneak attack forever?
Hey, Get up!: A full-round action? I'm not sure this'd get used over magical healing. Why not a standard action?
Move as one: This is very cool.
Of One Mind: Definitely a powerful capstone.

Some more possible bonuses (especially if you remove/move something):
Distracting feint; you may feint as a move action (or as a swift action if you have Improved Feint). You do not gain any bonuses from this feint; instead the opponent is flat-footed for your partner's next attack.
Improved Move as One: Not only do you and your partner act on the same initiative you may take your actions in any order (ie. you may make a standard action, followed by his move action, followed by your move, then his standard)
Uncanny Dodge: I just think this class should have it as some point. Maybe only when close to the partner though?
Have This: You may pass, or throw, your partner any useful item/weapon as an immediate action. Their catching it is also an immediate action. Weapons or tools thus passed are immediately usable.